The Effect of Sea Spray Evaporation on Tropical Cyclone Boundary Layer Structure and Intensity* (original) (raw)
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Boundary-Layer Meteorology, 2015
The impact of new parametrizations for drag and air-sea enthalpy exchange on modelling the intensity of tropical cyclones with a numerical weather prediction (NWP) model is examined. These parametrizations follow from a model for the marine atmospheric boundary layer for high wind-speed conditions in the presence of spray droplets that originate from breaking wave crests. This model accounts for the direct impact of these droplets on the air-sea momentum flux through action of a spray force, which originates from the interaction of the 'rain' of spray droplets with the vertical wind shear and is expressed in terms of the spray generation function (SGF). The SGF is cubic in the wind speed up to 50 m s −1 beyond which its value increases less strongly. The drag coefficient (C D) decreases from a wind speed of approximately 30 m s −1 , in agreement with the available measurements in these conditions. The enthalpy exchange coefficient (C k) increases with increasing wind speed and slowly decreases beyond a wind speed of about 40 m s −1 due to the strong decrease in C D. The value for C k /C D is in agreement with observational data for wind speeds up to 30 m s −1 ; for higher wind speeds the value is in the range 1.2-1.5 in agreement with a well-established theory. The parametrization is tested in an NWP model. The tropical cyclones Ivan (2004) and Katrina (2005) in the Gulf of Mexico are simulated. To the sea surface temperatures (SSTs) from the European Centre archive that were prescribed to the NWP model, a parametrized cooling (based on estimations from theoretical studies and measurements) was applied during the
2017
This paper addresses the issue of sea spray effects using a coupled atmosphere-wave model. The advantage of using a wave model is that sea spray production can be linked directly to the wave properties. The effects of sea spray are implemented for momentum, sensible heat, and latent heat fluxes. The spray production parameterization is a fixed droplet spectrum scaled by whitecap fraction (this follows most approaches in the literature). The major advance in this paper is the use of Anguelova and Hwang’s whitecap parameterization that is based on wave properties (taken from the wave model). The thermodynamic effects are implemented following the Andreas
Numerical Study on the Effect of the Ocean on Tropical-Cyclone Intensity and Structural Change
Atmospheric Model Applications, 2012
Atmospheric Model Applications 44 mesovortices and vortex Rossby waves. Mesovortices and vortex merger events are directly affected by SSC, which slows the formation of an annular potential-vorticity (PV) ring, whereas SST changes have little effect on the radius of maximum wind speed (MWS) at the mature phase of a TC when the annular PV ring is completely formed, even though mature TCs continue to cool the underlying ocean (Wada, 2009). TC-induced SSC is caused mostly by vertical turbulent mixing in the oceanic mixed layer and upwelling below a seasonal thermocline. In addition, strong wind stresses that accompany TCs cause variations in sea state or surface roughness length, leading to changes in frictional velocity and exchange coefficients for drag and enthalpy. Breaking surface waves are caused by variations of sea state under high winds and the resultant high waves. The breaking surface waves play an essential role in mechanical mixing near the surface (Wada et al., 2010). However, improvement of vertical turbulent mixing schemes and parameterizations in the ocean model is a challenging issue owing to a lack of in situ observations under high winds. Changes in exchange coefficients lead to changes in surface wind stresses and turbulent heat fluxes from the ocean to the atmosphere. The change in turbulent heat fluxes, particularly latent heat flux, enhances the secondary circulation of a TC through a planetary-boundarylayer process (Emanuel, 1986; Smith, 2008). In particular, turbulent heat fluxes vertically transferred from the warm ocean affect cloud microphysics and atmospheric radiation in the middle to upper troposphere, causing latent heat release through condensation, thus resulting in the formation of a warm core within the inner core of a TC.
Impact of Sea Spray on Numerical Simulation of Extratropical Hurricanes
2002
Although the question as to whether or how sea spray affects the evolution of hurricanes has been around a long time, the answer has been remained elusive. Over 50 years ago, Riehl (1954) suggested that the sea spray provides a significant amount of the heat needed to generate and maintain a tropical storm. Since the 1970s, a new wave of scientists rediscovered the sea spray problem (Wu, 1973, 1974; Bortkovskii, 1973; Ling and Kao 1976). With the more resent Humidity Exchange over the Sea (HEXOS) program, new ideas, better instruments, and more powerful analytical tools were brought to bear on the study of sea spray (Katsaros et al., 1987; Smith, 1988; Rouault et al., 1991). However, despite the huge HEXOS effort, parameterization of sea spray and its contribution to heat fluxes at high wind speeds remains a challenging task, because the data are still quite scanty. Andreas (1992) developed a simple model for the contribution of sea spray to sensible and latent heat fluxes. Fairall ...
Effects of surface heat flux-induced sea surface temperature changes on tropical cyclone intensity
Geophysical Research Letters, 2003
It is known that in deep and open oceans, the effect of sea surface sensible and evaporative heat fluxes on the tropical cyclone-induced sea surface cooling is small compared to that caused by turbulent mixing and cold water entrainment into the upper ocean mixed-layer. This study shows that tropical cyclone-induced surface heat fluxes dominate the surface cooling in near-coastal shallow ocean regions with limited or no underlying cold water. The thermal response of the ocean to the surface heat fluxes is nearly one dimensional through very quick vertical mixing in the ocean mixed layer. The flux-induced sea surface cooling may lead to appreciable reduction of storm intensity if the storm moves slowly. It is therefore important to account this negative feedback of ocean coupling in nearcoastal regions for more skillful forecasting of landfalling tropical cyclones.
Large-eddy simulation studies of sea spray in the hurricane atmospheric boundary layer
2007
The growth and maintenance of hurricanes is highly dependent upon the exchange of heat and momentum between the ocean and atmosphere. Because sea spray can significantly affect this ocean-air exchange, accurate hurricane models need to account for spray effects. We incorporate sea spray into large-eddy simulations (LES) to explore its role in the atmospheric boundary layer (ABL) of hurricanes, allowing us to assess the validity of and offer improvements to the simple spray parameterizations currently used in hurricane models. We investigate thermodynamic feedback between spray and surface heat fluxes, and examine the effects of spray upon the dynamics of the hurricane boundary layer. Results of preliminary LES, which use a bulk representation of the dominant range of spray sizes and a simplified diagnostic phase change scheme, indicate an appreciable amount of spray-air heat transfer-consistent with theory-and demonstrate a form of spray-induced thermodynamic feedback. The LES model of the hurricane atmospheric boundary layer (HABL) is adapted to account for variations in spray generation due to wave-breaking, momentum transfer between air and spray in both the vertical (liquid loading and stratification) and horizontal (drag), and dissipative heating in an emulsion-like two-phase environment. These modifications are accompanied by extension of the phase change and spray generation schemes to account for different droplet sizes, and implementation of a moving three-dimensional boundary. Collective inclusion of all these pieces of modeled physics in the LES provides results which offer a better view of the limitations of current spray-flux models, and motivates a simpler and improved alternative model. The refined results of the 'full' LES-HABL model are consistent with early simulations, and underscore the significance of boundary-layer scale thermodynamic balance, spray-induced fluxes, and wind-dependent thermodynamic feedback. iii 1 Introduction 1 2 Review of literature 4 2.1 Hurricanes and the role of sea spray. .. .. .. .. .. .. .. .. . 4 2.2 Large-eddy simulation of the moist atmosphere with phase change. 5 2.2.1 Modeling phase change in large-eddy simulations. .. .. .. 6 2.2.2 Previous applications of large-eddy simulation with phase change;
Simulation of extratropical Hurricane Gustav using a coupled atmosphere-ocean-sea spray model
Geophysical Research Letters, 2004
1] Numerical simulations of extratropical Hurricane Gustav (2002) are performed using the MC2 (Mesoscale Compressible Community) atmospheric model, coupled to the Princeton Ocean Model (POM), and a sea spray parameterization. On one hand, the impact of coupling POM to MC2 generates sea surface temperature (SST) cooling, through entrainment mixing at the bottom of the mixed layer, with the passage of the storm. SST cooling reduces the sea surface heat fluxes compared to uncoupled MC2 simulations, which have time-invariant SST. Reduced heat fluxes lead to reduced storm intensity. On the other hand, simulation of the heat and mass flux contributions of sea spray enhances sea surface heat fluxes and slightly increases maximum storm intensity compared to coupled MC2-POM simulations without spray. INDEX TERMS: 0312 Atmospheric Composition and Structure: Air/sea constituent fluxes (3339, 4504); 3339 Meteorology and Atmospheric Dynamics: Ocean/atmosphere interactions (0312, 4504); 4504 Oceanography: Physical: Air/sea interactions (0312).
Sea Spray Impacts on Intensifying Midlatitude Cyclones
Journal of the Atmospheric Sciences, 2005
Air–sea transfer processes over the ocean strongly affect how hurricanes develop. High winds generate large amounts of sea spray, which can modify the transfer of momentum, heat, and moisture across the air–sea interface. However, the extent to which sea spray can modify extratropical or midlatitude hurricanes and intense cyclones has not been resolved. This paper reports simulations of extratropical Hurricanes Earl (1998) and Danielle (1998) and an intense winter cyclone from January 2000 using a mesoscale atmospheric model and a recent sea spray parameterization. These simulations show that sea spray can increase the sea surface heat flux, especially the latent heat flux, in a midlatitude cyclone and that sea spray’s impact on cyclone intensity depends on the storm structure and development and is strongest for cyclones with high winds.
Parameterizations of Sea-Spray Impact on the Air–Sea Momentum and Heat Fluxes
Monthly Weather Review, 2011
This paper focuses on parameterizing the effect of sea spray at hurricane-strength winds on the momentum and heat fluxes in weather prediction models using the Monin-Obukhov similarity theory (a common framework for the parameterizations of air-sea fluxes). In this scheme, the mass-density effect of sea spray is considered as an additional modification to the stratification of the near-surface profiles of wind, temperature, and moisture in the marine surface boundary layer (MSBL). The overall impact of sea-spray droplets on the mean profiles of wind, temperature, and moisture depends on the wind speed at the level of sea-spray generation. As the wind speed increases, the mean droplet size and the mass flux of sea-spray increase, rendering an increase of stability in the MSBL and the leveling-off of the surface drag. Sea spray also tends to increase the total air-sea sensible and latent heat fluxes at high winds. Results from sensitivity testing of the scheme in a numerical weather prediction model for an idealized case of hurricane intensification are presented along with a dynamical interpretation of the impact of the parameterized sea-spray physics on the structure of the hurricane boundary layer.
The Formation of Concentric Eyewalls with Heat Sink in a Simple Tropical Cyclone Model
Terrestrial, Atmospheric and Oceanic Sciences, 2006
A linearized, two-layer axisymmetric model analogous to Schubert el al. (1980) is used to simulate the formation of concentric eyewalls in an ideal strong tropical cyclone. By imposing a heat sink near the center of a cyclone the induced perturbation wind, through thermodynamic adjustment to the heat sink, forms a double-peak structure when the disturbance is added to the basic state tangential wind. The heat sink represents, in a crude way, evaporative cooling of precipitation falling from cloud during late stage convective activity or a cooling through environmental advection. Detailed profiling of the induced double-peak wind structure is dependent on the radial profile of the imposed heat sink. After the double-peak tangential wind structure is formed, if a heat source corresponding to a new convective activity is generated inside the outer maximum tangential wind, the outer eyewall contracts and strengthens while the inner eyewall weakens. This result suggests that thermodynamic adjustments to changes in the heating of a tropical-cyclone-core region may contribute to the formation of the double-eyewall phenomenon.